1. Field of the Invention
The present invention generally relates to a silicon-on-insulator (SOI) semiconductor device, and more particularly, to an SOI semiconductor device capable of preventing floating body effect of the SOI device and method of manufacturing the same.
2. Description of the Related Art
As semiconductor devices have high performance, the SOI substrate (hereinafter "SOI device") has been suggested remarkably instead of silicon substrate made of bulk silicon. The SOI substrate comprises a handling wafer as a supporting part, a buried insulating layer and a semiconductor layer on which a device is formed later. An SOI device formed on an SOI substrate is completely isolated by a buried oxide layer and field oxide layer, and a junction capacitance is reduced, thereby achieving low power consumption and fast operation.
FIG. 1 is a cross-sectional view showing a conventional SOI device in which a transistor is formed. As shown in the drawing, an SOI substrate 10 comprising a handling wafer 11, a buried insulating layer 12 and a semiconductor layer 13, is provided. A field oxide layer 14 is formed on a selected portion of the semiconductor layer 13 of the SOI substrate 10 thereby defining an active region. A bottom of the field oxide layer 14 is in contact with the buried insulating layer 12. A gate electrode 16 having a gate insulating layer 15 is formed at a selected portion of the semiconductor layer 13, and a sidewall spacer 17 is formed of an insulating layer at both sidewalls of the gate electrode 16. Junction regions 18a, 18b are formed at the semiconductor layer 13 of both sidewalls of the gate electrode 16. Bottoms of the junction regions 18a, 18b are in contact with the buried insulating layer 12.
In a transistor formed on such SOI substrate, the junction regions 18a, 18b are in contact with the buried insulating layer 12 and the junction capacitance is lower than the bulk silicon device, thereby performing fast operation. Further, if thickness of the semiconductor layer 13 is below 100 nm, on-current of transistor can be increased.
However, if the semiconductor layer 13 on which a transistor is formed later is separated by the field oxide layer 14 and the buried insulating layer 12, and the semiconductor layer 13 is formed of thin film, then potential within a channel region is higher than that within a conventional MOS transistor when the channel layer is completely depleted. Moreover, a potential barrier between source region and the channel region is lowered. Holes generated by the impact ions of the depletion layer at the drain side, are temporarily stored in the channel region. By doing so, potential in the channel region is raised and electrons are rapidly injected from the source region to the channel region. Thus, the floating body effect, i.e. a decrease of voltage between the source and the drain regions, occurs. The floating body effect causes malfunction of semiconductor device.